1. Field of the Invention
The present invention relates to a resonant transducer, a method of producing the resonant transducer, and an ultrasonic treatment tool including the resonant transducer, and more particularly, to a resonant transducer that can achieve a high vibration speed, a method of producing the resonant transducer, and an ultrasonic treatment tool including the resonant transducer.
2. Description of the Related Art
In recent years, an incision site is required to be as small as possible in medical practice in terms of an early recovery after surgery and a reduction in burden on a patient, and endoscopic surgery is actively adopted as the solution. For the endoscopic surgery, various surgical tools have been developed, and the application range thereof is becoming increasingly wider. Under such a circumstance, an ultrasonic knife is expected as one of the tools for endoscopic surgery.
With regard to ultrasonic treatment tools as described above, Japanese Patent Application Laid-Open No. 2002-65689 describes an ultrasonic treatment tool that ultrasonically vibrates a treating part by means of: a piezoelectric element that generates ultrasonic vibration; a horn part that increases the amplitude of the generated ultrasonic vibration; and a probe that transmits the vibration.
In addition, “Enhancement of Vibration Amplitude of Micro Ultrasonic Scalpel using PZT Film”, Minoru KUROSAWA and Takeshi SASANUMA, Technical Report of The Institute of Electronics, Information and Communication Engineers (IEICE), US2009-109(213)31 proposes a micro ultrasonic scalpel for use in endoscopic surgery, the micro ultrasonic scalpel using longitudinal vibration (vibration that is substantially perpendicular to the surface of a biological body to be cut). The longitudinal vibration is excited in a d31 mode of a piezoelectric film, and a sensor device for detecting the vibration speed can be incorporated.
In the ultrasonic treatment tool described in Japanese Patent Application Laid-Open No. 2002-65689, a bolted Langevin vibrator is used for the piezoelectric element in order to achieve a high vibration speed. Unfortunately, the vibration speed is not high enough to enable the ultrasonic treatment tool to perform incision and clotting, and hence the horn part that increases the vibration speed is necessary. In order to increase the vibration speed by the horn part, however, the size of the vibrating portion needs to be larger than that of the treating part. Accordingly, in consideration of actual use of the ultrasonic treatment tool in an endoscope, the size of the vibrating portion is limited to about 2 mm to 3 mm in diameter, and hence the treating part needs to be smaller than this size, resulting in an increase in treatment time. In addition, “Enhancement of Vibration Amplitude of Micro Ultrasonic Scalpel using PZT Film” describes a rectangular configuration without a horn part and a configuration with a horn part having a transformation ratio of 3.5, and also describes that the vibration speed of the vibrating portion is 2 m/s in the case of the rectangular configuration and is 7 m/s in the case of the configuration with the horn part. In order to enable the ultrasonic treatment tool to perform incision and clotting, the vibration speed of 7 m/s is necessary, and hence the transformation ratio needs to be set to be equal to or more than 3.5. In this case, the width of the treating part is smaller than 1 mm. In addition, the torque of the vibration is reduced in accordance with the transformation ratio, and hence the torque is unfavorably small.
The present invention has been made in view of the above-mentioned circumstances, and therefore has an object to provide a resonant transducer that can achieve a high vibration speed, a method of producing the resonant transducer, and an ultrasonic treatment tool including the resonant transducer.